Inertial sensor

ABSTRACT

An inertial sensor includes: a plurality of inertial force detection elements each configured to output an output signal corresponding to a detected inertial force; and a processor configured to execute processing relating to the output signal from each of the plurality of inertial force detection elements. The plurality of inertial force detection elements includes: a plurality of main inertial force detection elements configured to detect inertial forces of a plurality of first predetermined axes orthogonal to each other; and a sub-inertial force detection element configured to detect an inertial force of a second predetermined axis which intersects the plurality of first predetermined axes such that the second predetermined axis is orthogonal to none of the plurality of first predetermined axes.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is the U.S. National Phase under 35 U.S.C. § 371 ofInternational Patent Application No. PCT/JP2021/023941, filed on Jun.24, 2021 which in turn claims the benefit of Japanese Patent ApplicationNo. 2020-109128, filed on Jun. 24, 2020, the entire disclosures of whichApplications are incorporated by reference herein.

TECHNICAL FIELD

The present disclosure relates to inertial sensors. Specifically, thepresent disclosure relates to an inertial sensor for use in variouselectronic devices.

BACKGROUND ART

Patent Literature 1 discloses an angular velocity sensor which is a typeof inertial sensor. The angular velocity sensor of Patent Literature 1includes a tuning fork-type oscillator whose basic skeleton is made ofan elastic material such as a silicon, an IC chip, a package in whichthe tuning fork-type oscillator and the IC chip are housed and which ismade of ceramic, a lid for sealing the package, a holder integrallymolded of a resin together with the package sealed with the lid, a chippart, a conductor such as a terminal, and a case covering the holder.

In Patent Literature 1, failure diagnosis for a detector of the tuningfork-type oscillator is made possible to improve the reliability of theangular velocity sensor. However, in the angular velocity sensor ofPatent Literature 1, the IC chip is newly provided with a terminal towhich a check signal for the failure diagnosis for the detector of thetuning fork-type oscillator is externally supplied. Thus, the angularvelocity sensor of Patent Literature 1 has to be changed in itsstructure on an element level, which complicates the structure as awhole.

CITATION LIST Patent Literature

-   Patent Literature 1: JP 2010-107518 A

SUMMARY OF INVENTION

It is an object to provide an inertial sensor having improvedreliability while the structure of the inertial sensor is suppressedfrom being complicated

An inertial sensor according to an aspect of the present disclosureincludes: a plurality of inertial force detection elements eachconfigured to output an output signal corresponding to a detectedinertial force; and a processor configured to execute a process relatingto the output signal from each of the plurality of inertial forcedetection elements. The plurality of inertial force detection elementsinclude: a plurality of main inertial force detection elementsconfigured to detect inertial forces of a plurality of firstpredetermined axes orthogonal to each other; and a sub-inertial forcedetection element configured to detect an inertial force of a secondpredetermined axis which intersects the plurality of first predeterminedaxes such that the second predetermined axis is orthogonal to none ofthe plurality of first predetermined axes.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a block diagram of an inertial sensor according to anembodiment of the present disclosure;

FIG. 2 is a schematic plan view of the inertial sensor;

FIG. 3 is a schematic sectional view of the inertial sensor;

FIG. 4 is a schematic illustrative view of a tilted part of the inertialsensor;

FIG. 5 is an illustrative view of the relationship between a secondpredetermined axis and first predetermined axes of the inertial sensor;and

FIG. 6 is a schematic plan view of an inertial sensor of a variation.

DESCRIPTION OF EMBODIMENTS

An embodiment of the present disclosure will be described hereinafterwith reference to the drawings in some cases. The embodiment describedbelow is illustrative for describing the present disclosure and is notintended to limit the present disclosure to the following contents.

The relative positions and other positional relationships comply withthe drawings unless otherwise specified. Note that the drawings to bereferred to in the following description of the embodiment are allschematic representations, that is, the ratio of the dimensions(including thicknesses) of respective constituent elements illustratedon the drawings does not always reflect their actual dimensional ratio.In addition, the dimensional ratio of each element is not limited to theratio illustrated in the drawings.

In the present disclosure, an inertial sensor is a sensor that detectsan inertial force. The inertial force is expressed in acceleration inthe translationally accelerated system and in an angular velocity in therotating coordinate system. That is, detection of the inertial forcemeans detection of at least one of the acceleration or the angularvelocity. In this regard, the inertial sensor is a sensor that detectsat least one of the acceleration or the angular velocity.

(1) Embodiment

(1-1) Overview

FIG. 1 is a block diagram of an inertial sensor 10 according to thepresent embodiment. The inertial sensor 10 includes a plurality ofinertial force detection elements 40 and a processor 30. The pluralityof inertial force detection elements 40 output output signalscorresponding to respective detected inertial forces. The processor 30executes a process relating to the output signals from the plurality ofinertial force detection elements 40. The plurality of inertial forcedetection elements 40 include a plurality of main inertial forcedetection elements (second to fourth inertial force detection elements42 to 44) and a sub-inertial force detection element (first inertialforce detection element 41). The plurality of main inertial forcedetection elements (second to fourth inertial force detection elements42 to 44) detect inertial forces of a plurality of first predeterminedaxes (first to third axes A21 to A23, see FIGS. 2 and 3 ) orthogonal toone another. The sub-inertial force detection element (first inertialforce detection element 41) detects an inertial force of a secondpredetermined axis A11 (see FIGS. 2 and 3 ) which intersects theplurality of first predetermined axes A21 to A23 such that the secondpredetermined axis A11 is orthogonal to none of the plurality of firstpredetermined axes A21 to A23.

In the inertial sensor 10 of the present embodiment, the plurality ofinertial force detection elements 40 include the sub-inertial forcedetection element (first inertial force detection element 41) inaddition to the plurality of main inertial force detection elements(second to fourth inertial force detection elements 42 to 44). Theplurality of main inertial force detection elements (second to fourthinertial force detection elements 42 to 44) detect the inertial forcesof the plurality of first predetermined axes (first to third axes A21 toA23) orthogonal to one another, whereas the sub-inertial force detectionelement 41 detects the inertial force of the second predetermined axisA11 which intersects the plurality of first predetermined axes (first tothird axes A21 to A23) such that the second predetermined axis A11 isorthogonal to none of the plurality of first predetermined axes.Therefore, the inertial force detected by the sub-inertial forcedetection element (first inertial force detection element 41) caninclude a component of the respective inertial force detected by each ofthe plurality of main inertial force detection elements (second tofourth inertial force detection elements 42 to 44). Therefore, thesub-inertial force detection element can be utilized in failurediagnosis for the plurality of main inertial force detection elements,and moreover, in case of failures in the plurality of main inertialforce detection elements, the sub-inertial force detection element canbe used in place of the plurality of inertial force detection elements.This can be achieved by simply adding the sub-inertial force detectionelement to the plurality of inertial force detection elements 40. Thus,according to the inertial sensor 10 of the present application, thereliability is improved while the structure of the inertial sensor issuppressed from being complicated

(1-2) Configurations

A detection system 1 according to the present embodiment will bedescribed hereinafter in detail referring to the drawings.

As shown in FIG. 1 , the inertial sensor 10 includes a sensor unit 20and the processor 30.

The sensor unit 20 includes the plurality of inertial force detectionelements 40 and a plurality of drive circuits 50.

The plurality of inertial force detection elements 40 detect inertialforces and output output signals corresponding to the respectiveinertial forces thus detected. Each of the plurality of inertial forcedetection elements 40 is a mechano-electrical transduction element(e.g., Micro Electro Mechanical Systems: MEMS). Each of the plurality ofinertial force detection elements 40 is an angular velocity detectionelement. Each of the plurality of inertial force detection elements 40detects an angular velocity as the inertial force. Since the structureof each inertial force detection element 40 may be a structure of aconventionally well-known angular velocity detection element, thedetailed description thereof will be omitted.

The plurality of inertial force detection elements 40 include the firstinertial force detection element 41, the second inertial force detectionelement 42, a third inertial force detection element 43, and a fourthinertial force detection element 44. The first inertial force detectionelement 41 is the sub-inertial force detection element, and the secondto fourth inertial force detection elements 42 to 44 are the maininertial force detection elements.

The second inertial force detection element 42 detects an inertial forceof a first axis A21 (see FIGS. 2 and 3 ) and outputs an output signalcorresponding to the inertial force thus detected. In the presentembodiment, the second inertial force detection element 42 is an angularvelocity detection element. The inertial force of the first axis A21 isan angular velocity around the first axis A21.

The third inertial force detection element 43 detects an inertial forceof a second axis A22 (see FIGS. 2 and 3 ) and outputs an output signalcorresponding to the inertial force thus detected. The second axis A22is orthogonal to the first axis A21. In the present embodiment, thethird inertial force detection element 43 is an angular velocitydetection element. The inertial force of the second axis A22 is anangular velocity around the second axis A22.

The fourth inertial force detection element 44 detects an inertial forceof a third axis A23 (see FIGS. 2 and 3 ) and outputs an output signalcorresponding to the inertial force thus detected. The third axis A23 isorthogonal to each of the first axis A21 and the second axis A22. In thepresent embodiment, the fourth inertial force detection element 44 is anangular velocity detection element. The inertial force of the third axisA23 is an angular velocity around the third axis A23.

The first to third axes A21 to A23 are a plurality of (in thisembodiment, three) first predetermined axes orthogonal to one another.

The first inertial force detection element 41 detects the inertial forceof the second predetermined axis A11 (see FIGS. 2 and 3 ) and outputs anoutput signal corresponding to the inertial force thus detected. In thepresent embodiment, the first inertial force detection element 41 is anangular velocity detection element. The inertial force of the secondpredetermined axis A11 is an angular velocity around the secondpredetermined axis A11.

The second predetermined axis A11 intersects the first to third axes A21to A23 which are the first predetermined axes such that the secondpredetermined axis A11 is orthogonal to none of the first to third axesA21 to A23 as shown in FIGS. 4 and 5 . In the present embodiment, thesecond predetermined axis A11 is tilted by an angle θ from the firstaxis A21 on a plane (plane orthogonal to the second axis A22) includingthe first axis A21 and the third axis A23 as shown in FIG. 5 . Thesecond predetermined axis A11 is tilted by an angle φ from the firstaxis A21 on a plane (plane orthogonal to the third axis A23) includingthe first axis A21 and the second axis A22 as shown in FIG. 5 . Thus,the inertial force of the second predetermined axis A11 can containcomponents of the inertial forces of the first to third axes A21 to A23.

The plurality of inertial force detection elements 40 (41 to 44) havethe same detection ranges. The detection range is a detection range ofthe inertial force (the angular velocity in the present embodiment). Inparticular, in the present embodiment, the detection range is intendedto a range in which a change in the output signal of each inertial forcedetection element 40 in response to the change in the inertial force isregarded as having linearity. For example, the detection range of eachinertial force detection element 40 is greater than or equal to 0 andless than or equal to 200 [deg/sec].

The plurality of inertial force detection elements 40 (41 to 44) havethe same sensitivities. The sensitivity is, for example, the amount ofchange in the output with respect to a unit input. As for the angularvelocity, the sensitivity is the amount of change in the output signalwhen the angular velocity changes by 1 “deg/sec”. The higher thesensitivity, the easier a minute change in the angular velocity isdetected.

The plurality of inertial force detection elements 40 (41 to 44) havethe same bias stabilities. The bias stability is, for example, themagnitude of the variation in the output signal when the inertial forceis zero (at rest). High bias stability reduces erroneous detection whenthe inertial force is zero.

The plurality of drive circuits 50 give the output signals from theplurality of inertial force detection elements 40 to the processor 30.In the present embodiment, the plurality of drive circuits 50 drive theplurality of inertial force detection elements 40 to cause the pluralityof inertial force detection elements 40 to output output signalscorresponding to the respective inertial force thus detected. Each ofthe plurality of drive circuits 50 is, for example, an ApplicationSpecific Integrated Circuit (ASIC). Since the structure of each drivecircuit 50 may be the structure of a drive circuit for conventionallywell-known angular velocity detection elements, the detailed descriptionthereof will be omitted.

The plurality of drive circuits 50 include two drive circuits 51 and 52.The drive circuit 51 acquires the output signal from the first inertialforce detection element 41 and gives the output signal to the processor30. The drive circuit 52 acquires the output signals from the second tofourth inertial force detection elements 42 to 44 and gives the outputsignals to the processor 30. As shown in FIGS. 2 and 3 , each of the twodrive circuits 51 and 52 is generally rectangular plate-shaped. Thedrive circuit 51 corresponds to a first drive circuit, and the drivecircuit 52 corresponds to a second drive circuit. The output signalwhich the drive circuit 51 acquires from the first inertial forcedetection element 41 corresponds to a first output signal. The outputsignals which the drive circuit 52 acquires from the second to fourthinertial force detection elements 42 to 44 correspond to second outputsignals.

As shown in FIGS. 1 to 3 , the sensor unit 20 includes two sensorelements 21 and 22. The sensor element 21 includes the first inertialforce detection element 41 of the plurality of inertial force detectionelements 40. The sensor element 22 includes the second inertial forcedetection element 42, the third inertial force detection element 43, andthe fourth inertial force detection element 44 of the plurality ofinertial force detection elements 40. The second inertial forcedetection element 42, the third inertial force detection element 43, andthe fourth inertial force detection element 44 are integrated into onepiece. Thus, the plurality of main inertial force detection elements areelements integrally formed as one piece. As shown in FIGS. 2 and 3 , thetwo sensor elements 21 and 22 are generally rectangular plate-shaped.

The sensor unit 20 further includes a package 60 as shown in FIGS. 2 and3 .

The package 60 houses the two sensor elements 21 and 22 and the twodrive circuits 51 and 52. The package 60 includes a base 61 and a cover62. The two sensor elements 21 and 22 and the two drive circuits 51 and52 are housed in a space between the base 61 and the cover 62. In FIG. 2, the cover 62 is omitted.

The base 61 has an arrangement surface on which the two sensor elements21 and 22 and the two drive circuits 51 and 52 are arranged. Thearrangement surface includes a main arrangement surface 610 a and asub-arrangement surface 91 which are in different orientations. The mainarrangement surface 610 a and the sub-arrangement surface 91 will bedescribed later.

The base 61 includes a base part 610 and a sidewall part 611. Both thebase part 610 and the sidewall part 611 are electrically insulating. Thebase part 610 and the sidewall part 611 are formed as a continuous onepiece. For example, the base part 610 and the sidewall part 611 are amolded article made of an electrically insulating resin. The base part610 has the main arrangement surface 610 a constituting part of thearrangement surface. The base part 610 has a rectangular plate shape.The base part 610 has a surface constituting the main arrangementsurface 610 a. The surface is one surface in a thickness direction. Thesidewall part 611 protrudes from the outer periphery of the one surfacein the thickness direction defined with respect to the base part 610.The sidewall part 611 has a rectangular frame shape. The cover 62 isattached to the sidewall part 611 so as to face the main arrangementsurface 610 a of the base part 610. The cover 62 has a rectangular plateshape. The cover 62 is electrically insulating. For example, the cover62 is a molded article made of an electrically insulating resin.

The base 61 further includes an anti-vibration portion 70, a pluralityof connecting members 80, and a tilted part 90.

The anti-vibration portion 70 is arranged on the main arrangementsurface 610 a of the base 61. In particular, the anti-vibration portion70 lies between the main arrangement surface 610 a and the two sensorelements 21 and 22 and the two drive circuits 51 and 52. Theanti-vibration portion 70 is provided to reduce the influence of avibration outside the package 60 on the two sensor elements 21 and 22.This reduces noise generated in the inertial sensor 10. For example, theanti-vibration portion 70 is made of an elastic and electricallyinsulating material.

The plurality of connecting members 80 are used for electricalconnection of at least the drive circuits 51 and 52 to the processor 30.Each of the plurality of connecting members 80 includes an electrodeportion 81 and a terminal portion 82. The plurality of connectingmembers 80 are embedded in the base 61. In each connecting member 80,the electrode portion 81 is exposed at the main arrangement surface 610a of the base part 610, the terminal portion 82 protrudes outward from aside surface of the base part 610. The electrode portions 81 of theplurality of connecting members 80 are used for electrical connection tothe drive circuits 51 and 52. The terminal portions 82 of the pluralityof connecting members 80 are used for electrical connection to theprocessor 30. In the present embodiment, the plurality of connectingmembers 80 are held by the base 61 by insert molding.

The tilted part 90 is on a surface, constituting the main arrangementsurface 610 a, of the base 61. In the present embodiment, the tiltedpart 90 is on the anti-vibration portion 70 on the base 61. The tiltedpart 90 has a tilted surface constituting the sub-arrangement surface91. The sub-arrangement surface 91 constitutes part of the arrangementsurface.

The two sensor elements 21 and 22 and the two drive circuits 51 and 52are arranged on the arrangement surface of the base 61. As shown inFIGS. 2 and 3 , the two drive circuits 51 and 52 are arranged on theanti-vibration portion 70 on the arrangement surface of the base 61. Inthe present embodiment, the two drive circuits 51 and 52 are alignedalong the length direction (left/right direction in FIG. 2 ) of the base61. The drive circuit 52 is arranged on the anti-vibration portion 70 onthe main arrangement surface 610 a. The sensor element 22 is arranged onan opposite side of the drive circuit 52 from the main arrangementsurface 610 a. The sensor element 22 is connected in electricalconnection to the drive circuit 52 by one or more conductive wires W21.The drive circuit 52 is connected in electrical connection tocorresponding one or more of the electrode portions 81 respectively byone or more conductive wires W22. The drive circuit 51 is arranged onthe sub-arrangement surface 91. The sensor element 21 is arranged on anopposite side of the drive circuit 51 from the sub-arrangement surface91. The sensor element 21 is connected in electrical connection to thedrive circuit 51 by one or more conductive wires W11. The drive circuit51 is connected in electrical connection to corresponding one or more ofthe electrode portions 81 respectively by one or more conductive wiresW12.

The sensor element 22 is on the main arrangement surface 610 a, and thesensor element 21 is on the sub-arrangement surface 91. The sensorelement 22 includes the second to fourth inertial force detectionelements 42 to 44, which are the plurality of main inertial forcedetection elements, and therefore, the plurality of inertial forcedetection elements are on the main arrangement surface 610 a. The sensorelement 21 includes the first inertial force detection element 41, whichis the sub-inertial force detection element, and therefore, thesub-inertial force detection element is on the sub-arrangement surface91.

As shown in FIGS. 2 and 3 , the first axis A21 of the second inertialforce detection element 42 is orthogonal to the main arrangement surface610 a. The second axis A22 and the third axis A23 are orthogonal to thefirst axis A21, and therefore, the main arrangement surface 610 a is aplane including the second axis A22 and the third axis A23. The secondaxis A22 of the third inertial force detection element 43 is along thewidth direction of the base 61 (up/down direction in FIG. 2 ). Inparticular, the second axis A22 of the third inertial force detectionelement 43 is orthogonal to a direction in which the two sensor elements21 and 22 (two drive circuits 51 and 52) are aligned (left/rightdirection in FIG. 2 ). The third axis A23 of the fourth inertial forcedetection element 44 is along the length direction of the base 61(left/right direction in FIG. 2 ). In particular, the third axis A23 ofthe fourth inertial force detection element 44 is orthogonal to adirection in which the two sensor elements 21 and 22 (two drive circuits51 and 52) are aligned (left/right direction in FIG. 2 ).

As shown in FIG. 4 , the second predetermined axis A11 of the firstinertial force detection element 41 is orthogonal to the sub-arrangementsurface 91. The sub-arrangement surface 91 is tilted by an angle θ withrespect to a plane (main arrangement surface 610 a) including the secondaxis A22 and the third axis A23 when viewed from the second axis A22.Moreover, the sub-arrangement surface 91 is titled by an angle φ withrespect to the plane (main arrangement surface 610 a) including thesecond axis A22 and the third axis A23 when viewed from the third axisA23. Thus, the second predetermined axis A11 is tilted by the angle θfrom the first axis A21 on the plane (plane orthogonal to the secondaxis A22) including the first axis A21 and the third axis A23. Thesecond predetermined axis A11 is tilted by the angle φ from the firstaxis A21 on the plane (plane orthogonal to the third axis A23) includingthe first axis A21 and the second axis A22.

The processor 30 executes a process relating to the output signals fromthe plurality of inertial force detection elements 40. The processor 30acquires, from the drive circuits 51 and 52, the output signals from theplurality of inertial force detection elements 40. The processor 30acquires the output signals from the plurality of inertial forcedetection elements 40 at a predetermined interval. The predeterminedinterval is at least accordingly set in accordance with thesensitivities and the like of the plurality of inertial force detectionelements 40.

The processor 30 obtains the inertial force of the first predeterminedaxis (first axis A21) with reference to the output signal from thesecond inertial force detection element 42. The processor 30 obtains theinertial force of the first predetermined axis (the second axis A22)with reference to the output signal from the third inertial forcedetection element 43. The processor 30 obtains the inertial force of thefirst predetermined axis (the third axis A23) with reference to theoutput signal from the fourth inertial force detection element 44. Insum, the processor 30 obtains the inertial forces of the three firstpredetermined axes (the first to third axes A21 to A23) orthogonal toone another (angular velocities around the first to third axes A21 toA23), that is, the angular velocities of the three axis with referenceto the output from the sensor element 22.

The processor 30 obtains the inertial force of the second predeterminedaxis A11 with reference to the output signal from the first inertialforce detection element 41. In sum, the processor 30 obtains theinertial force of the second predetermined axis A11 (angular velocityaround the second predetermined axis A11), that is, the angular velocityof the one axis with reference to the output from the sensor element 21.

The processor 30 executes a diagnostic process. The diagnostic processis a process of performing failure diagnosis for the plurality of maininertial force detection elements with reference to the output signalfrom the sub-inertial force detection element. That is, the processor 30performs failure diagnosis for the second to fourth inertial forcedetection elements 42 to 44 with reference to the output signal of thefirst inertial force detection element 41. As described above, theinertial force of the second predetermined axis A11 can includecomponents of the inertial forces of the first to third axes A21 to A23.Thus, when the angles θ and φ are known, the inertial force of each ofthe first to third axes A21 to A23 is obtainable from the inertial forceof the second predetermined axis A11. When none of the second to fourthinertial force detection elements 42 to 44 has a failure, the inertialforces of the second to fourth inertial force detection elements 42 to44 each obtained from the inertial force of the second predeterminedaxis A11 obtained from the output signal from the first inertial forcedetection element 41 are respectively equal to the inertial forcesobtained from the output signals from the second to fourth inertialforce detection elements 42 to 44. Thus, when a component of a specificfirst predetermined axis of the plurality of first predetermined axes(first to third axes A21 to A23) obtainable from the inertial forcebased on the output signal from the sub-inertial force detection element(first inertial force detection element 41) does not match an inertialforce based on an output signal from a specific main inertial forcedetection element corresponding to the specific first predetermined axisand included in the plurality of main inertial force detection elements(second to fourth inertial force detection elements 42 to 44), theprocessor 30 determines that the specific main inertial force detectionelement has a failure. Specifically, if the inertial force of the firstaxis A21 obtained from the output signal (inertial force of the secondpredetermined axis A11) from the first inertial force detection element41 does not match the inertial force from the second inertial forcedetection element 42 corresponding to the first axis A21, the processor30 determines the occurrence of a failure in the second inertial forcedetection element 42. If the inertial force of the second axis A22obtained from the output signal (inertial force of the secondpredetermined axis A11) from the first inertial force detection element41 does not match the inertial force from the third inertial forcedetection element 43 corresponding to the second axis A22, the processor30 determines the occurrence of a failure in the third inertial forcedetection element 43. If the inertial force of the third axis A23obtained from the output signal (inertial force of the secondpredetermined axis A11) from the first inertial force detection element41 does not match the inertial force from the fourth inertial forcedetection element 44 corresponding to the third axis A23, the processor30 determines the occurrence of a failure in the fourth inertial forcedetection element 44. If the occurrence of a failure in any of the maininertial force detection elements (second to fourth inertial forcedetection elements 42 to 44) is determined as a result of the diagnosticprocess, the processor 30 issues a notification of the occurrence of thefailure.

Note that as a method of performing the failure diagnosis, the inertialforces of the plurality of main inertial force detection elementsobtained from the inertial force based on the output signal from thesub-inertial force detection element are compared with the inertialforces based on the output signals from the main inertial forcedetection elements, but instead of this method, the inertial force basedon the output signal from the sub-inertial force detection element maybe compared with a combined inertial force obtained by combining theinertial forces based on the output signals from the plurality of maininertial force detection elements. For example, when the angles θ and φare known, a component of the second predetermined axis A11 can beobtained from a combined inertial force obtainable from the inertialforces of the first to third axes A21 to A23. When none of the second tofourth inertial force detection elements 42 to 44 has a failure, theinertial force of the second predetermined axis A11 obtained from theoutput signal from the first inertial force detection element 41 isequal to the component of the second predetermined axis A11 of thecombined inertial force obtained from the output signals from the secondto fourth inertial force detection elements 42 to 44. If the componentof the second predetermined axis A11 of the combine inertial force fromthe second to fourth inertial force detection elements 42 to 44 does notmatch the inertial force of the second predetermined axis A11 obtainedfrom the output signal from the first inertial force detection element41, the processor 30 determines the occurrence of a failure in any ofthe plurality of main inertial force detection elements (second tofourth inertial force detection elements 42 to 44). If the occurrence ofa failure in any of the main inertial force detection elements isdetermined as a result of the diagnostic process, the processor 30issues a notification of the occurrence of the failure. In this case,however, the output signals have to be output from the plurality of maininertial force detection elements before the inertial forces arecombined with each other.

As described above, if the processor 30 determines, as a result of thediagnostic process, that none of the plurality of main inertial forcedetection elements has a failure, the processor 30 outputs the inertialforces of the plurality of first predetermined axes (first to third axesA21 to A23) obtained with reference to the output signals from thesecond to fourth inertial force detection elements 42 to 44. If theprocessor 30 determines, as a result of the diagnostic process, theoccurrence of a failure in any of the plurality of main inertial forcedetection elements, the processor issues a notification of theoccurrence of the failure.

(2) Variations

The embodiment of the present disclosure is not limited to theembodiment described above. The embodiment described above may bereadily modified in various manners depending on a design choice or anyother factor without departing from the scope of the present disclosure.Variations of the embodiment described above will be enumerated below.The variations described below are applicable accordingly incombination.

FIG. 6 shows an inertial sensor 10A of a variation. The inertial sensor10A includes a sensor unit 20A and a processor 30 (see FIG. 1 ).

The sensor unit 20A includes a plurality of inertial force detectionelements and a plurality of drive circuits 50 (51 and 52A).

The plurality of inertial force detection elements include two maininertial force detection elements and a sub-inertial force detectionelement. Also in this variation, the plurality of inertial forcedetection elements are angular velocity detection elements.

The two main inertial force detection elements detect inertial forces ofa plurality of first predetermined axes (second and third axes A22 andA23, see FIG. 6 ) orthogonal to each other. The sub-inertial forcedetection element detects an inertial force of a second predeterminedaxis A11 which intersects the plurality of first predetermined axes A22and A23 such that the second predetermined axis A11 (see FIG. 6 ) isorthogonal to none of the first predetermined axes A22 and A23.

The plurality of drive circuits 50 includes the two drive circuits 51and 52A. The drive circuit 52A acquires output signals from the two maininertial force detection elements and gives the output signals to theprocessor 30. The drive circuit 52A is generally rectangularplate-shaped.

A sensor element 21 includes the sub-inertial force detection element. Asensor element 22A includes the two main inertial force detectionelements. The two main inertial force detection elements are integratedinto one piece. As shown in FIG. 6 , the two sensor elements 21 and 22Aare generally rectangular plate-shaped.

The two sensor elements 21 and 22A and the two drive circuits 51 and 52Aare arranged on an arrangement surface of a base 61. As shown in FIG. 6, the two drive circuits 51 and 52A are arranged on an anti-vibrationportion 70 on the arrangement surface of the base 61. The two drivecircuits 51 and 52A are aligned along a length direction (left/rightdirection in FIG. 6 ) of the base 61. The drive circuits 51 and 52A arearranged on the anti-vibration portion 70 on the arrangement surface ofthe base 61.

The sensor element 22A is arranged on an opposite side of the drivecircuit 52A from the arrangement surface. The sensor element 22A isconnected in electrical connection to the drive circuit 52A by one ormore conductive wires W21. The drive circuit 52A is connected inelectrical connection to corresponding one or more of the electrodeportions 81 respectively by one or more conductive wires W22. The sensorelement 21 is arranged on an opposite side of the drive circuit 51 fromthe arrangement surface. The sensor element 21 is connected inelectrical connection to the drive circuit 51 by one or more conductivewires W11. The drive circuit 51 is connected in electrical connection tocorresponding one or more of the electrode portions 81 respectively byone or more conductive wires W12.

As shown in FIG. 6 , the second and third axes A22 and A23 which are thefirst predetermined axes of the two main inertial force detectionelements are included in the arrangement surface. The second axis A22 isalong a width direction (up/down direction in FIG. 6 ) of the base 61.In particular, the second axis A22 is orthogonal to a direction(left/right direction in FIG. 6 ) in which the two sensor elements 21and 22A (two drive circuits 51 and 52A) are aligned. The third axis A23is along a length direction (left right direction in FIG. 6 ) of thebase 61. In particular, the third axis A23 is along the direction(left/right direction in FIG. 6 ) in which the two sensor elements 21and 22A (two drive circuits 51 and 52A) are aligned.

In the sensor element 21, the second predetermined axis A11 of thesub-inertial force detection element is orthogonal to the thickness ofthe sensor element 21. In addition, the sensor element 21 is arranged onthe arrangement surface such that the second predetermined axis A11 isincluded in the arrangement surface and intersects the second axis A22and the third axis A23 such that the second predetermined axis A11 isorthogonal to none of the second axis A22 and the third axis A23 (seeFIG. 6 ). In an example, the second predetermined axis A11 is in thearrangement surface and intersects each of the second axis A22 and thethird axis A23 at 45 degrees.

In the variation, the processor 30 (see FIG. 1 ) obtains the inertialforces of the first predetermined axes (the second axis A22 and thethird axis A23) based on the output signals from the two main inertialforce detection elements. In sum, the processor 30 obtains the inertialforces of the two first predetermined axes (the second and third axesA22 and A23) orthogonal to each other (angular velocities around thesecond and third axes A22 and A23), that is, angular velocities of thetwo axes with reference to an output from the sensor element 22A. Theprocessor 30 obtains the inertial force of the second predetermined axisA11 with reference to the output signal from the sub-inertial forcedetection element. In sum, the processor 30 obtains the inertial forceof the second predetermined axis A11 (angular velocity around the secondpredetermined axis A11), that is, an angular velocity of the one axiswith reference to an output from the sensor element 21.

As described above, the inertial force of the second predetermined axisA11 can include components of the inertial forces of the second andthird axes A22 and A23. Thus, if the angle of the second predeterminedaxis A11 with respect to the second and third axes A22 and A23 is known,a component of the second predetermined axis A11 is obtainable from acombined inertial force obtained from the inertial forces of the secondand third axes A22 and A23. Therefore, the processor 30 can perform thefailure diagnosis for the two main inertial force detection elementswith reference to the output signal from the sub-inertial forcedetection element.

In a similar manner to the embodiment described above, the processor 30executes the diagnostic process, and if the processor 30 determines, asa result of the diagnostic process, that none of the two main inertialforce detection elements has a failure, the processor 30 outputs theinertial forces of the plurality of first predetermined axes (second andthird axes A22 and A23) obtained with reference to the output signalsfrom the two main inertial force detection elements. If the processor 30determines, as a result of the diagnostic process, the occurrence of afailure in any of the two main inertial force detection elements, theprocessor 30 issues a notification of the occurrence of the failure.

Next, some other variations will be enumerated.

In a variation, the first predetermined axes are not limited to thefirst to third axes A21 to A23. The first predetermined axes are notlimited to the first axis A21, the second axis A22, and the third axisA23 but may be axes of arbitrary angles.

In a variation, at least two of the plurality of inertial forcedetection elements 40 may have detection ranges different from eachother. For example, the first inertial force detection element 41 mayhave a detection range which is different from the detection ranges ofthe second to fourth inertial force detection elements 42 to 44.

In a variation, at least two of the plurality of inertial forcedetection elements 40 may have sensitivities different from each other.For example, the first inertial force detection element 41 may havesensitivity different from the sensitivities of the second to fourthinertial force detection elements 42 to 44.

In a variation, at least two of the plurality of inertial forcedetection elements 40 may have bias stabilities different from eachother. For example, the first inertial force detection element 41 mayhave a bias stability different from the bias stabilities of the secondto fourth inertial force detection elements 42 to 44.

In a variation, the processor 30 may acquire the output signals from theplurality of inertial force detection elements 40 at intervals differentfrom each other. For example, the processor 30 may acquire the outputsignal from the first inertial force detection element 41 at an intervaldifferent from the intervals at which the output signals are acquiredfrom the second to fourth inertial force detection elements 42 to 44.

In a variation, each of the plurality of inertial force detectionelements 40 may be an acceleration detection element. Each of theplurality of inertial force detection elements 40 detects anacceleration as the inertial force. The structure of each inertial forcedetection element may be a structure of a conventionally well-knownacceleration detection element, and thus, the detailed descriptionthereof will be omitted.

In a variation, the plurality of inertial force detection elements 40may include a plurality of angular velocity detection elements and aplurality of acceleration detection elements. The plurality of angularvelocity detection elements may include two or more angular velocitydetection elements that detect angular velocity around the same axis.The plurality of acceleration detection elements may include two or moreacceleration detection elements that detect accelerations of the sameaxes.

In a variation, the plurality of main inertial force detection elementsdo not necessarily have to be integrated into one sensor element. Eachof the plurality of sensor elements may include a single inertial forcedetection element.

In a variation, each of the drive circuit 50 is not limited to an ASICbut may be, for example, a Field-Programmable Gate Array (FPGA) or maybe configured by one or more processors and one or more memory elements.One drive circuit 50 may control a plurality of sensor elements.

In a variation, in the inertial sensor 10, the number of the maininertial force detection elements is not particularly limited and is anynumber that is at least two or grater, and the number of thesub-inertial force detection elements is not particularly limited and isany number that is at least one or greater. The plurality of inertialforce detection elements 40 may include a plurality of combinations ofthe plurality of inertial force detection elements and sub-inertialforce detection elements.

In a variation, the sub-inertial force detection element may be utilizedin place of a main inertial force detection element having a failure ofthe plurality of main inertial force detection elements. When a specificmain inertial force detection element of the plurality of main inertialforce detection elements has a failure, the processor 30 may output,based on the output signal from the sub-inertial force detectionelement, the inertial force of the first predetermined axiscorresponding to the specific main inertial force detection element ofthe plurality of first predetermined axes. For example, if it isdetermined, as a result of the diagnostic process, that the secondinertial force detection element 42 has a failure, the processor 30outputs the angular velocity around the first axis A21 obtained from thefirst inertial force detection element 41 instead of the angularvelocity around the first axis A21 obtained from the second inertialforce detection element 42. Therefore, even in case of a failure of themain inertial force detection element, the inertial sensor 10 cancontinue operating. Thus, the processor 30 may obtain an inertial forceof at least one of the plurality of first predetermined axes withreference to the output signal from the sub-inertial force detectionelement.

In a variation, the plurality of inertial force detection elements 40may include a plurality of sub-inertial force detection elements. Theplurality of sub-inertial force detection elements may have differentsecond predetermined axes. The plurality of sub-inertial force detectionelements can include a sub-inertial force detection element for failuredetermination and a sub-inertial force detection element for areplacement for a main inertial force detection element.

(3) Aspects

As can be seen from the embodiment and the variations described above,the present disclosure includes the following aspects. In the followingdescription, reference signs in parentheses are added only to clarifythe correspondence relationship to the embodiment.

A first aspect is an inertial sensor (10; 10A) and includes a pluralityof inertial force detection elements (40) each configured to output anoutput signal corresponding to a detected inertial force; and aprocessor (30) configured to execute a process relating to the outputsignal from each of the plurality of inertial force detection elements(40). The plurality of inertial force detection elements (40) include aplurality of main inertial force detection elements (42 to 44) and asub-inertial force detection element (41). The plurality of maininertial force detection elements (42 to 44) are configured to detectinertial forces of a plurality of first predetermined axes (A21 to A23)orthogonal to each other. The sub-inertial force detection element (41)is configured to detect an inertial force of a second predetermined axis(A11) which intersects the plurality of first predetermined axes (A21 toA23) such that the second predetermined axis (A11) is orthogonal to noneof the plurality of first predetermined axes (A21 to A23). This aspectenables the reliability to be improved while the structure is suppressedfrom being complicated.

A second aspect is an inertial sensor (10) referring to the firstaspect. In the second aspect, the inertial sensor (10) further includesa base (61) having an arrangement surface (610 a, 91). The arrangementsurface (610 a, 91 includes a main arrangement surface (610 a) and asub-arrangement surface (91) which are in different orientations. Theplurality of main inertial force detection elements (42 to 44) are onthe main arrangement surface (610 a). The sub-inertial force detectionelement (41) is on the sub-arrangement surface (91). This aspectfacilitates setting of the second predetermined axis (A11).

A third aspect is an inertial sensor (10) referring to the secondaspect. In the third aspect, the base (61) includes a base part (610)having a surface constituting the main arrangement surface (610 a) and atilted part (90) on the surface, the tilted part (90) having a tiltedsurface constituting the sub-arrangement surface (91). This aspectfacilitates setting of the second predetermined axis (A11).

A fourth aspect is an inertial sensor (10) referring to any one of thefirst to third aspects. In the fourth aspect, the plurality of firstpredetermined axes (A21 to A23) further includes a third axis (A23)orthogonal to each of the first axis (A21) and the second axis (A22).According to this aspect, inertial forces of the three axes areobtainable from the main inertial force detection elements.

A fifth aspect is an inertial sensor (10; 10A) referring to any one ofthe first to fourth aspects. In the fifth aspect, the processor (30) isconfigured to perform failure diagnosis for the plurality of maininertial force detection elements (42 to 44) with reference to an outputsignal from the sub-inertial force detection element (41). This aspectenables the reliability to be improved.

A sixth aspect is an inertial sensor (10; 10A) referring to the fifthaspect. In the sixth aspect, the processor (30) is configured to, when acomponent of a specific first predetermined axis of the plurality offirst predetermined axes (A21 to A23) obtainable from an inertial forcebased on the output signal from the sub-inertial force detection element(41) does not match an inertial force based on an output signal from aspecific main inertial force detection element corresponding to thespecific first predetermined axis and included in the plurality of maininertial force detection elements (42 to 44), determine that thespecific main inertial force detection element has a failure. Thisaspect enables the reliability to be improved.

A seventh aspect is an inertial sensor (10; 10A) referring to the fifthaspect. In the seventh aspect, the processor (30) is configured todetermine that at least one of the plurality of main inertial forcedetection elements (42 to 44) has a failure when an inertial force basedon the output signal from the sub-inertial force detection element (41)does not match a component of a combined inertial force obtained bycombining a plurality of output signals from the plurality of maininertial force detection elements (42 to 44). This aspect enables thereliability to be improved.

An eighth aspect is an inertial sensor (10; 10A) referring to any one ofthe first to seventh aspects. In the eighth aspect, the processor (30)is configured to, when a specific main inertial force detection elementof the plurality of main inertial force detection elements (42 to 44)has a failure, obtain an inertial force of a first predetermined axiscorresponding to the specific main inertial force detection element andincluded in the plurality of first predetermined axes (A21 to A23) withreference to an output signal from the sub-inertial force detectionelement (41). This aspect enables the reliability to be improved.

A ninth aspect is an inertial sensor (10; 10A) referring to any one ofthe first to eighth aspects. In the ninth aspect, each of the pluralityof inertial force detection elements (40) is a mechano-electricaltransduction element. This aspect enables the inertial sensor (10; 10A)to be downsized.

A tenth aspect is an inertial force sensor (10; 10A) referring to anyone of the first to ninth aspects. In the tenth aspect, the inertialsensor (10; 10A) further includes a plurality of drive circuits (50)each configured to give the output signal from a corresponding one ofthe plurality of inertial force detection elements (40) to theprocessor. The plurality of drive circuits (50) includes a first drivecircuit (51) configured to acquire a first output signal from thesub-inertial force detection element (41) and give the first outputsignal to the processor (30) and a second drive circuit (52; 52A)configured to acquire second output signals from the plurality of maininertial force detection elements (42 to 44) and give the second outputsignals to the processor (30). The processor (30) is configured toexecute a process relating to the first output signal and the secondoutput signals as the process relating to the output signal.

An eleventh aspect is an inertial force sensor (10; 10A) referring tothe tenth aspects. In the eleventh aspect, the inertial sensor (10; 10A)further includes a base (61) having an arrangement surface (610 a, 91).The arrangement surface (610 a, 91) includes a main arrangement surface(610 a) and a sub-arrangement surface (91) which are in differentorientations. The first drive circuit (51) is on the sub-arrangementsurface (91). The second drive circuit (52) is on the main arrangementsurface (610 a).

A twelfth aspect is an inertial sensor (10; 10A) referring to the secondor third or eleventh aspect. In the thirteenth aspect, the base (61)includes an anti-vibration portion (70) lying between the mainarrangement surface (610 a) and the plurality of inertial forcedetection elements (40).

REFERENCE SIGNS LIST

-   10; 10A Inertial Sensor-   30 Processor-   40 Inertial Force Detection Element-   41 First Inertial Force Detection Element (Sub-Inertial Force    Detection Element)-   42 Second Inertial Force Detection Element (Main Inertial Force    Detection Element)-   43 Third Inertial Force Detection Element (Main Inertial Force    Detection Element)-   44 Fourth Inertial Force Detection Element (Main Inertial Force    Detection Element)-   50 Drive Circuit-   51 Drive Circuit (First Drive Circuit)-   52; 52A Drive Circuit (Second Drive Circuit)-   61 Base-   610 a Main Arrangement Surface-   70 Anti-Vibration Portion-   90 Tilted Part-   91 Sub-Arrangement Surface-   A21 First Axis (First Predetermined Axis)-   A22 Second Axis (First Predetermined Axis)-   A23 Third Axis (First Predetermined Axis)-   A11 Second Predetermined Axis

1. An inertial sensor comprising: a plurality of inertial forcedetection elements each configured to output an output signalcorresponding to a detected inertial force; and a processor configuredto execute a process relating to the output signal from each of theplurality of inertial force detection elements, the plurality ofinertial force detection elements including a plurality of main inertialforce detection elements configured to detect inertial forces of aplurality of first predetermined axes orthogonal to each other and asub-inertial force detection element configured to detect an inertialforce of a second predetermined axis which intersects the plurality offirst predetermined axes such that the second predetermined axis isorthogonal to none of the plurality of first predetermined axes.
 2. Theinertial sensor of claim 1, further comprising a base having anarrangement surface, wherein the arrangement surface includes a mainarrangement surface and a sub-arrangement surface which are in differentorientations, the plurality of main inertial force detection elementsare on the main arrangement surface, and the sub-inertial forcedetection element is on the sub-arrangement surface.
 3. The inertialsensor of claim 2, wherein the base includes a base part having asurface constituting the main arrangement surface and a tilted part onthe surface, the tilted part having a tilted surface constituting thesub-arrangement surface.
 4. The inertial sensor of claim 1, wherein theplurality of first predetermined axes are three axes orthogonal to oneanother.
 5. The inertial sensor of claim 1, wherein the processor isconfigured to perform failure diagnosis for the plurality of maininertial force detection elements with reference to an output signalfrom the sub-inertial force detection element.
 6. The inertial sensor ofclaim 5, wherein the processor is configured to, when a component of aspecific first predetermined axis of the plurality of firstpredetermined axes obtainable from an inertial force based on the outputsignal from the sub-inertial force detection element does not match aninertial force based on an output signal from a specific main inertialforce detection element corresponding to the specific firstpredetermined axis and included in the plurality of main inertial forcedetection elements, determine that the specific main inertial forcedetection element has a failure.
 7. The inertial sensor of claim 5,wherein the processor is configured to determine that at least one ofthe plurality of main inertial force detection elements has a failurewhen an inertial force based on the output signal from the sub-inertialforce detection element does not match a component of a combinedinertial force obtained by combining a plurality of output signals fromthe plurality of main inertial force detection elements.
 8. The inertialsensor of claim 1, wherein the processor is configured to, when aspecific main inertial force detection element of the plurality of maininertial force detection elements has a failure, obtain an inertialforce of a first predetermined axis corresponding to the specific maininertial force detection element and included in the plurality of firstpredetermined axes with reference to an output signal from thesub-inertial force detection element.
 9. The inertial sensor of claim 1,wherein each of the plurality of inertial force detection elements is amechano-electrical transduction element.
 10. The inertial sensor ofclaim 1, further comprising a plurality of drive circuits eachconfigured to give the output signal from a corresponding one of theplurality of inertial force detection elements to the processor, whereinthe plurality of drive circuits includes a first drive circuitconfigured to acquire a first output signal from the sub-inertial forcedetection element and give the first output signal to the processor anda second drive circuit configured to acquire second output signals fromthe plurality of main inertial force detection elements and give thesecond output signals to the processor, and the processor is configuredto execute a process relating to the first output signal and the secondoutput signals as the process relating to the output signal.
 11. Theinertial sensor of claim 10, further comprising a base having anarrangement surface, wherein the arrangement surface includes a mainarrangement surface and a sub-arrangement surface which are in differentorientations, the first drive circuit is on the sub-arrangement surface,and the second drive circuit is on the main arrangement surface.
 12. Theinertial sensor of claim 2, wherein the base includes an anti-vibrationportion lying between the main arrangement surface and the plurality ofinertial force detection elements.
 13. The inertial sensor of claim 3,wherein the base includes an anti-vibration portion lying between themain arrangement surface and the plurality of inertial force detectionelements.
 14. The inertial sensor of claim 11, wherein the base includesan anti-vibration portion lying between the main arrangement surface andthe plurality of inertial force detection elements.
 15. The inertialsensor of claim 2, wherein the plurality of first predetermined axes arethree axes orthogonal to one another.
 16. The inertial sensor of claim3, wherein the plurality of first predetermined axes are three axesorthogonal to one another.
 17. The inertial sensor of claim 2, whereinthe processor is configured to perform failure diagnosis for theplurality of main inertial force detection elements with reference to anoutput signal from the sub-inertial force detection element.
 18. Theinertial sensor of claim 3, wherein the processor is configured toperform failure diagnosis for the plurality of main inertial forcedetection elements with reference to an output signal from thesub-inertial force detection element.
 19. The inertial sensor of claim4, wherein the processor is configured to perform failure diagnosis forthe plurality of main inertial force detection elements with referenceto an output signal from the sub-inertial force detection element. 20.The inertial sensor of claim 15, wherein the processor is configured toperform failure diagnosis for the plurality of main inertial forcedetection elements with reference to an output signal from thesub-inertial force detection element.